1. Field of the Invention
The invention is related to computing systems and more particularly to connections in computing systems.
2. Description of the Related Art
In general, devices in a computing system communicate via a logical connection called an interconnect or link. A typical link compliant with an exemplary link protocol is a point-to-point communication channel between two ports including one or more lanes. An individual lane is composed of a transmit and receive pair of lines. The lines may be single-ended lines or differential lines. In at least one embodiment of a link, each lane includes a transmit and receive pair of differential lines, i.e., each lane includes four signal paths between endpoints of the link, to support full duplex communications. An exemplary low-speed device uses a single-lane link, while an exemplary higher-speed device (e.g., graphics adapter) uses a much wider, multi-lane link.
In at least one embodiment, a link implements serial communications, which is less affected by timing skew as compared to parallel communications links since serial links do not require that the bits of a particular word of data arrive at their destination simultaneously. The technique of serial communications sends data one bit at a time, sequentially over the communication link. Exemplary serial communications links include Peripheral Component Interconnect Express (PCIE), HyperTransport (formerly known as Lightning Data Transport), Serial Advanced Technology Attachment (Serial ATA), universal serial bus (USB), IEEE 1394 interface, Serial RapidIO, and Serial Attached Small Computer System Interface (SAS)). In at least one embodiment of a processing system, more than one type of serial communications link is used (e.g., PCIE and HyperTransport). HyperTransport is a protocol for interconnection of computer processors using a bidirectional, serial, high-bandwidth, low-latency, point-to-point link. A typical HyperTransport link supports bit widths that range from two to thirty-two bits. However, a HyperTransport link requires sideband control and command signals. In addition, HyperTransport is a DC-coupled link. Peripheral Component Interconnect Express (PCIE) is a computer expansion card standard, typically used as a board-level interconnect (e.g., to link to motherboard mounted peripherals) and used as an expansion card interface for add-in boards. Typical PCIE slots contain from one to sixteen lanes and are AC-coupled. Each lane typically includes one pair of transmit differential signals and one pair of receive differential signals. In general, HyperTransport and PCIE links support substantially the same data rates.
An exemplary processing system includes a printed circuit board assembly (e.g., motherboard, backplane, or other printed circuit board assembly) having an expansion slot (i.e., slot) for adding functionality to the processing system. An exemplary expansion board (i.e., expansion card, adapter card, or accessory card) includes a device (e.g., processor or peripheral device). In at least one embodiment, an expansion slot couples a component (e.g., a device or an expansion board) to the printed circuit board using a connector that is compliant with a communications link protocol used by a processor or device on the printed circuit board assembly and used by the component.
In at least one embodiment, the processing system and connector are included in a blade server. As referred to herein, a blade server (i.e., blade) is a printed circuit board assembly including a processor, memory, I/O, and non-volatile storage elements. A typical blade server has a modular design that reduces the use of physical space and energy as compared to other server systems. A typical blade enclosure includes multiple blades to form a blade system and provides one or more of power, cooling, networking, interconnects, and management for the system. A manufacturer packages a complete server with its operating system and applications on a single blade. The blade can operate independently within a chassis common to multiple blades.